Mass Transfer and Chemical Reaction in Liquid-Liquid Agitation Systems

The objectives of the agitation of liquid-liquid mass transfer systems with or without chemical reaction may be set forth as follows in general : (1) increase in the inter facial area by promoting dispersion, (2) diminution of the mass transfer resistance in the diffusion film outside the liquid droplets, and (3) diminution of the mass transfer resistance in the inner part of liquid droplets or mixing of dispersed phase. The diameter of liquid droplets was measured to estimate the interfacial area. At the same time, the rate of reaction or the rate of mass transfer was observed for various kinds of liquid-liquid mass transfer systems which were classified according to reaction or no reaction and according to degree of difference in density. Comparison was then made between the increase in the estimated inter facial area and the increase in the rate of reaction caused by the increase in agitator speed. On the other hand, mathematical analysis were performed on these processes to clarify the effect of agitation for various kinds of fundamental and important liquid-liquid agitation systems. Thus the authors found that the effect of agitation upon the liquid-liquid mass transfer was mainly to increase the interfacial area, that the decrease of the mass transfer resistance in the diffusion film outside droplets was slight, and that the mixing of the inner part of the droplets was rather decreased by the increase in agitator speed. Part I Effect of Agitation for the Diminution of Mass Transfer Resistance in Continuous Phase

Rate of Solution of Solid Particles Followed by Chemical Reaction in Agitation Vessel

In this paper, the authors deal with the dissolution of acid anhydride in water followed by the hydrolysis reaction. Classification may be made of the types of reaction taking place depending upon the relative rates of diffusion and hydrolysis of the acid anhydride. (1) Diffusion resistance is controlling and the overall rate of reaction depends only on the rate of solution. In this case the higher the agitator speed, the larger the rate of solution. (2) Diffusion resistance and the chemical resistance to hydrolysis are comparable in magnitude. In this case the overall rate of reaction depends not only on the agitator speed, but also on the rate of hydrolysis. (3) Chemical resistance to hydrolysis is controlling and the overall rate of reaction is independent of the agitator speed. The authors derived the generalized rate equation and demonstrated the three types of reaction by the hydrolysis reaction of phthalic acid anhydride and benzoic acid anhydride suspended in water under agitation. The authors propose the idea of “the degree of transitional saturation” and “the agitation coefficient for heterogeneous reaction”. The latter is useful for the determination of the available agitation intensity for heterogeneous liquid phase reactions

Chemical Absorption of Gas into Liquid Film on Rotating Drum

With a rotating drum type gas-liquid contactor of known area, the effects of gas rate and the rotational speed of the drum on the thickness of liquid film were observed and the rate of gas absorption accompanied by a chemical reaction in the liquid phase was measured using either one of the catalysts, mannitol, Cu⁺⁺ and Co⁺⁺⁺. The analytical solution was presented for the simultaneous unsteady state absorption and (m+l)-st order reaction (m-th order with reactant A and 1st order with reactant B respectively). Experimental results were compared with theories and the five states of rate controlling were verified which had formerly been derived analytically. The five states correspond to the case where mass transfer are controlled by the resistances of ; (1) chemical reaction in the liquid, (2) both chemical reaction and diffusion in the liquid, (3) diffusion of the dissolved gas in the liquid film, (4) both diffusion and chemical reaction in the liquid film and (5) diffusion of the reactant from the liquid bulk. The rate constant of the accompanied reaction was also determined

Rate of Solution of Solid Particles in Agitated Liquids

Hixson and Baum have proposed generalized dimensionless equations for the rate of solution of solid particles in agitated liquids. The authors developed an improved equation and conducted additional experiments on the rates of solution of zinc and magnesium metals in dilute hydrochloric acid containing potassium nitrate. Experiments were also made on the rate of solution of benzoic acid in NaOH solutions and of sugar in water. The newly developed equation is as follows: (KD/Df)=α′(D²nρₗ/µ)ᵖ(µ/ρₗFf)q(δ³g/ν²)r(ρₛ-ρₗ/ρₗ)ᵗ The constant α′ and exponents p, q and s are presented in this paper. The authors arrived at the following conclusions: (1) At a definite critical Reynolds number, Rf (or agitator speed, Nf), solid particles are fluidized in an agitated liquid. (2) At this critical Reynolds number (or agitator speed), the rate of increase in solution velocity is abruptly decreased with further increase in agitator speed. (3) In the fluidized state where N>Nf, an increase in density difference between the solid and liquid phases combined with the effect of agitation velocity greatly reduces the diffusional resistance. (4) In the range of Reynolds numbers less than Rf, or agitator speed less than Nf, the apparent rate of solution of solid particles increases with the 1.0 to 1.4 power of Rₑ depending upon the conditions of agitation. This experimental effect may reach a value of even 2.9 for small particles. (5) From these experiments it is expected that the effect of agitation in liquid-liquid systems is mainly to increase the reaction surface area, and that the effect of agitation in diminishing diffusion resistance is rather small. The effect of agitation in solid-liquid systems in the range of fluidization is mainly to diminish diffusional resistance

Les stratégies des acteurs maritimes chinois en mer de Chine du Sud

Cet article a pour ambition de présenter la coordination des différents acteurs maritimes chinois en mer de Chine du Sud. Depuis environ 2009, la Chine a intensifié ses revendications territoriales maritimes dans cet espace et a pris des mesures coercitives, au rang desquelles figurent le harcèlement des navires étrangers et l’usage d’outils administratifs dans le but d’étendre son contrôle effectif sur des îles contestées. Une question importante qui se pose est de savoir si la tactique chinoise repose sur un plan concerté ou bien si elle est la conséquence involontaire de la concurrence entre les divers acteurs concernés et de la défense de leurs intérêts particuliers. Cet article montre premièrement qu’il y a de plus en plus de coordination organisationnelle entre ces acteurs, deuxièmement que l’Armée populaire de libération (APL) a un rôle de premier plan dans la conduite des opérations, et enfin qu’il semble s’agir d’une tendance à long terme. L’article conclut que les aspirations à long terme convergent désormais au sein de plans plus concrets sous la présidence de Xi Jinping

Strategies of China’s Maritime Actors in the South China Sea

This paper aims to explore the coordination among China’s various maritime actors in the South China Sea (SCS). Since around 2009, China has reinforced its maritime territorial claims in the SCS and has taken coercive measures, including harassing other countries’ vessels and using administrative tools to expand its effective control over disputed islands. One important question is whether China’s tactics are based on a well-coordinated plan or are the unintended consequence of competition and self-interest among the various agencies. This paper shows that, firstly, organisational coordination between these agencies is improving, secondly, that the PLA has a salient role in the operation, and lastly, that the long term trend is important. The paper implies that long-term aspirations are coalescing into more concrete plans under the strong leadership of Xi Jinping